Cisco and Comcast have also recently joined the WBA, which provides for easy roaming onto hot spots

AT&T and Verizon Wireless, the two largest U.S. mobile operators, have joined an organization that ensures roaming among mobile operators' Wi-Fi networks.

The group, called the Wireless Broadband Alliance (WBA), also announced on Monday that South Korean mobile operator KT, Cisco Systems, U.S. cable operator Comcast, and wireless software vendor Devicescape Software have recently joined.

The WBA provides for sharing of login credentials among operators of Wi-Fi networks so that subscribers can log into another WBA member's network using the same username and password as they do with their primary carrier. Service providers that join WBA commit to participating in this program over time, though the interoperability may not be available immediately, said Dave Fraser, CEO of Devicescape. AT&T and Verizon were not immediately able to confirm what they will be doing with the WBA.

As mobile data use rapidly grows and strains some cellular networks, carriers are trying to shift as much data as possible onto Wi-Fi where it is available. Both AT&T and Verizon make large networks of hot spots available to their subscribers. Eliminating username and password entry to get onto Wi-Fi hot spots is becoming more important as more subscribers access Wi-Fi from smartphones rather than laptops, Fraser said.

Also on Tuesday, the WBA said it is set to release the WISPr 2.0 specification, which will allow Wi-Fi network operators to go beyond the single-login capability and remove the need for entering any username and password for roaming. The new specification, designed by the WBA, also will allow for roaming from a 3G (third-generation) or 4G (WiMax or LTE) network on to Wi-Fi. The aim is to automatically shift a user's data activity onto Wi-Fi wherever available, whether the user is in the coverage area of the primary carrier or a roaming partner, Fraser said.

However, neither interoperability program eliminates roaming charges among carriers, he added.

The WBA will be conducting trials of WISPr 2.0 for about six months, and it is unlikely to be implemented commercially for at least one year, Fraser said.

Other WBA members include BT Group, Deutsche Telekom, NTT, Boingo Wireless, and Tata Communications Internet Services. Together, the service-provider members operate more than 100,000 Wi-Fi hot spots worldwide and have a combined subscriber base of more than 350 million, according to the WBA.